The present invention relates to a cylindrical electrophotographic photosensitive member.
In a conventional charging process for electrophotographic image-forming apparatuses, a contact-based charging apparatus has been widely used. In the contact-based charging apparatus, a charging member with a high voltage applied thereto is directly contacted with a surface of an electrophotographic photosensitive member to charge a photosensitive layer of the photosensitive member. In this case, the charging member is comprised of rollers or brushes.
Advantages of the contact method relative to the corona discharge method, which had been commonly used before the contact method has become popular, include a substantially reduced amount of ozone generation and a relatively simple and compact design for the structure of the apparatus.
One problem of the contact charging method is noise occurring during the charging operation. In general, in applying a voltage to the charging member, in the contact charging method, an appropriate alternating voltage is superposed on an underlying direct voltage to improve uniformity of charging on the surface of the photosensitive member. This alternating component may be the cause of charging-related noise, as it induces vibration between the charging member and the photosensitive member, with vibration levels varying with the applied alternating frequency (Japanese Patent Application Laid Open No. 4-86682). This noise depends on the condition of the apparatus, and is perceived as a relatively high sound by a person. This sound is very uncomfortable in a normal office environment, and should desirably be reduced to a level at which it no longer induces unpleasant effect on an office environment.
In a conventional well-known method effective for reducing the charging sound, a sound-absorbing member is placed inside the photosensitive drum (Japanese Patent Applications Laid Open No. 5-35166, No. 5-35167, No. 5-35048 and No. 8-54804).
FIG. 6 is a perspective view of a conventional cylindrical member made from resin. In this figure, the cylindrical resin member has a slit therein extending in an axial direction thereof, and the resin has a spring function so that the cylindrical member can be fixed inside the photosensitive drum in pressure contact therewith (Japanese Patent Application Laid Open No. 8-54804).
Although the above method with the cylindrical resin member is generally excellent in terms of its function, operability and economy, this cylindrical member is adversely affected when it is left in the environment, that is, it may lose its sound reduction effect depending on environmental conditions.
This problem arises from the stress constantly effected inside the photosensitive drum on a portion of the resin having the spring function (which is opposed to the slit). The trouble occurs particularly when the photosensitive drum is left in a high-temperature environment. Due to its creep property, the resin tends to become deformed over time regardless of the magnitude of the stress applied. In addition, as the environmental temperature increases, the resin and cylinder are expanded to thereby increase the stress level, and the resin itself becomes more likely to be deformed due to heat. In case a temperature returns to a room-temperature level after the cylindrical member has experienced the high-temperature environment, the pressure contact force decreases substantially as compared to the initial value, thereby reducing the member's sound reduction effect. Depending on the thermal conditions to which the cylindrical member is exposed and the duration, the pressure contact force may become zero to thereby prevent proper fixation. In this case, the member's muffling function is no longer provided. Such a high-temperature environment is assumed to exist during transportation or practical use of an image-forming apparatus.
The present invention has been made in view of these problems, and an object of the invention is to provide an electrophotographic photosensitive member comprising a cylindrical resin member fixed to a photosensitive drum to provide a pressure contact therewith, the photosensitive drum being subjected to the contact-charging method and having a charging-sound absorption capability, wherein the cylindrical resin member is not adversely affected when it is left in an adverse operating environment.